U.S. Pat. No. 5,491,373 to Cooper, et al., incorporated herein in its entirety by this reference, discloses an exemplary high-speed rotary switch or commutator. Denoted a "barrel-style" device, the commutator illustrated in the Cooper, et al. patent includes multiple electrically-conductive segments arranged into a cylinder on the outer diameter of a non-conductive core. An electrical brush passes along the outer diameter of the core to form a conductive path with the one or more segments in contact with it at any given instant.
Described in U.S. Pat. Nos. 5,760,518 and 5,826,324 to Abe, et al. (also incorporated herein in their entireties by this reference) is a commutator whose face, rather than outer diameter or edge, conducts electricity. This face-style commutator is an alternative to a barrel-style device and is often used in devices exposed to corrosive environments or immersed in fuel. FIGS. 1 and 2 of the Abe, et al. patents illustrate aspects of such a commutator, with electrically-conductive segments 3 consisting principally of graphite.
Also shown in FIG. 2 of the Abe, et al. patents is metal shell or plate 5, whose terminal 6 admits connection to windings of a motor, and an electrically-insulating support 1. Plate 5 includes on its inner surface "small projections 7," which function to anchor the graphite segments 3 from displacement as the commutator operates. According to the Abe, et al. patents, a separate, unillustrated "part of . . . metal plate 5 is embedded in the electrically insulating support 1" to retain the relative positions of the plate and support.
Listed on the faces of the Abe, et al. patents as their assignee is Aupac Co., Ltd. ("Aupac"). A commutator made by Aupac includes two sets of anchors in the plate or shell. One set, analogous to the unshown portions of metal plate 5 discussed in the Abe, et al. patents, retains the position of the insulating support or core of the commutator, while the other (analogous to "small projections 7") assists in anchoring the conductive segments relative to the plate or shell. However, unlike projections 7 of the Abe, et al. patents, which extend radially inward from an inner surface of the plate or shell, the analogous anchors of the Aupac commutator are formed by bending radially inward axially-extending protrusions on an edge of the plate or shell (rather than as protrusions from its side).
FIGS. 1-6 illustrate, essentially identically, aspects of the Aupac commutator 100. Detailed in FIGS. 1-3 is metal shell 104 in which anchors 108 are formed. Such anchors 108 extend radially inward from shell 104 and are used to moor an electrically-insulating core 110 (see FIG. 4). Also shown in FIGS. 1-3 are terminals 112 (which ultimately will be bent into tangs or hooks) and projections 116. As noted in the preceding paragraph, projections 116 are not formed in inner surface 120 of shell 104 but rather extend from its edge 124 before being bent inward.
Manufacture of the Aupac commutator 100 is relatively complex. Initially, shell 104 must be blanked and formed in the manner of FIGS. 1-3 so as to create anchors 108, terminals 112, and projections 116. Core 110 must then be molded into shell 104, as shown in FIG. 4, so that its phenolic material surrounds anchors 108. Molding core 110 in this manner effectively embeds anchors 108 therein, helping fix the position of core 110 relative to shell 104.
After the phenolic material of core 110 is molded and cured, excess material (typically denoted "flash") must be removed from inner surface 120. Failure to remove such excess material can be problematic, as it can adversely affect the electrical continuity between shell 104 and the electrically-conductive graphite segments 126 (see FIG. 6) ultimately forming the face of the Aupac commutator 100. Machining, furthermore, is required to delete flash from inner surface 120 once core 110 has been molded and cured.
After the material of core 110 is cured and the flash is removed from inner surface 120 of shell 104, projections 116 must be bent radially inward as illustrated in FIG. 5. Concurrently terminals 112 may be formed into tangs or hooks 128 for subsequent attachment to the windings of a motor. Only then are conductive segments 126 created as shown in FIG. 6.
Included in FIG. 6 are the segments 126, which initially consist of graphite powder or material. The material is molded, or pressed, into recess 132 (see FIG. 5) so that it abuts core 110 and projections 116 are embedded within. Doing so anchors the material of segments 126 to shell 104, after which the material is cured and slotted to form the segments 126.
Surface 136 contacts electrical brushes, and thereby wears, in use. As is readily visible in FIG. 6, a substantial portion of each segment 126 lies further from surface 136 than projections 116 (and thus is not within the depth D.sub.2 shown in that figure). It hence is unavailable as a contact surface, resulting in significant waste of the graphite material.
Moreover, to applicants' knowledge, at no time does shell 104 of the Aupac commutator 100 extend beyond surface 136. Shell 104 indeed cannot readily do so, as projections 116 must be bent inward in order to be embedded within segments 126. Similarly, neither commutator of the Abe, et al. patents contemplates having a plate 5 extending at any time above the exposed face of the carbonaceous material. Even though theoretically not impossible to extend plates 5 (upward as oriented in FIGS. 2 and 3 of the Abe, et al. patents) beyond pieces 3, no basis for such extension appears in the Abe, et al. patents.